The present invention generally relates to multiple phase electric motors, and more particularly to the winding of coils during the manufacture of such motors.
Conventional brushless permanent magnet servomotor designs that are common in the marketplace include 4-pole rotor-12 slot stator motors; 4 pole-24 slot motors; 6 pole-18 slot motors; and 6 pole-36 slot motors, for example. An illustration of an 18-slot stator 10 is shown in FIG. 1. A typical winding pattern for two phases (U and V) of an 18-slot stator is shown in FIGS. 2 and 3. Because of the crossovers 12 of coils in the ends of the stator 10, the winding end-turns 14 tend to be long and bulky and add considerably to the winding resistance in the winding pattern shown in FIG. 2. This reduces the motor torque density. Also, in order to produce motors capable of running off servo amplifier bus voltages up to approximately 680 V DC, inter-phase insulation paper 16 must be routed between the coils of adjacent phases.
To avoid these issues many manufacturers have adapted motor topologies using single-tooth winding, so that each coil has a span of one lamination tooth. In order to utilize this topology, the ratio of motor slots to poles (S/P) must lie in the range of 0.5<S/P≦1.5. Single tooth winding significantly reduces the height of the winding heads 14 and eliminates crossovers 12 between coils of different phases, as shown in FIG. 4.
Two design classes are practiced in the construction of single tooth windings, the first being single piece lamination with needle winding and the second being segmented stators. With regard to the single piece lamination with needle winding, this practice has the advantage that the stator laminations are whole or single piece, allowing easier assembly of the stator pack. Prestack stator packs are desirable for volume production. The windings are placed in the slots with a needle winder which somewhat restricts the available winding space.
With regard to the segmented stator winding practice, there are many variations on this theme but all involve a segmented stator pack. The windings are wound in very high density either directly on the tooth or on separate bobbins and subsequently transferred onto the tooth. Bobbin winding requires some sacrifice of available winding area in order to get good layering, but very high density windings can be achieved. There is, however, an extra step of recombining the stator segments after winding placement.
Stator connection refers to the process of linking all the coils in each of the phases. In a three-phase stator connection, a star-point is formed from the ends of the coils of each phase and the starts of the three phases are brought to the outside world as shown in FIG. 5. For small motors it is commonplace to terminate the start and finish of each coil on terminal posts.